How to login with new domain with Gmail Business

[Chaos27]

Im wondering as I have been asked to find out this.

A business gmail account was originally created ...@.... After a year or a few months later they decided to change it to a different domain. They have done that no problem. But the original email they sighed up with still exist. When they send an email it sends with the new domain email address.

What I would like to know is how to change the login to the new domain? And not use the old domain name that was originally created.?

[Macman]

Isn't the login just your username?

[Chaos27]

Yes it is but the email still exists. Its confusing for the person. Is there a way to change it to the present domain?

Thanks